Comparative Vertebrate Physiology

Action potentials

Neuron anatomy and signaling

Action potential

DepolarizationRepolarizationHyperpolarization

Action potential Phases

Resting membrane potential Depolarization Repolarization Hyperpolarization

Nernst equation Measures equilibrium potential Depends on:

absolute temperature valence ratio of concentration gradients

Ex =RTzF

In[X]I[X]II

Nernst equation

If [K]o = 0.01M and [K]I = 0.1M

Ex =0.058z

log[X]I[X]II

Ex =0.0581

log0.010.1

=−58mV

Action potential Hodgkin and Huxley theory

Resting membrane potential

Action potential Resting membrane potential

Action potential Hodgkin and Huxley theory

Depolarization: rising phase Na+ (5,000x)

Action potential Hodgkin and Huxley theory

Repolarization : falling phase K+ (10x)

Action potential Hodgkin and Huxley theory

Hyperpolarization

Membrane permeability

Protein gates Types

Chemical Occur between neurons

Voltage Occur within neurons

Voltage gates

Refractory period Absolute

Na+ activation gate open

Relative Na+ activation gate closed

Channel toxins TTX (tetradotoxin)

Japanese puffer fish decreases Na+conductance increases K+conductance

Channel toxins TEA (tetraethylammonium)

Synthetic organic compound increases Na+conductance decreases K+conductance

Channel toxins

Threshold An all-or-none event

Threshold

Factors effecting Magnitude Duration

Excitation curve

Volts

Milliseconds

1

1

2

2

3

3

4

4 5X

Chronaxie

A

B

C

Rheobase

Impulse conduction

Impulse conduction

Schwann cell secrete myelin

Conduction velocity

Mylenated: 15 - 40 msec-1

Unmylenated: 0.4 - 0.5 msec-1